KE / Momentum for Medium Plains Game?

[mdwest]

I am probably WAY over thinking this... but based on my last experience bow hunting PG with a bow (under penetration on a wildebeest that resulted in a LONG track.. several miles over a 24 hour period of time).. I am wanting to make sure I get things absolutely right this time around (Im taking a bow back to SA in July with the intent of hunting a few species of PG)..

Im shooting an older PSE Mach X bow.. arrows are CE Piledrivers with G5 Montec broadheads.. total arrow weight is 602 gr..

Im currently shooting at 65lbs.. speed is reliably chrono'd at 211 fps (not a super fast bow)..

Using the linked KE and Momentum calculator below.. im getting a KE value of 59.45 and a Momentum value of .564

My gut tells me this should be more than enough to effectively and humanely hunt up to medium sized PG to include the "tough" ones like wildebeest, zebra, etc..

Reading older threads on AH however.. it looks like the recommended KE for medium PG is 70 KE (Im a good bit short.. and even if I crank my bow up to its max 70lb draw capability, the max KE value I get is 63.71..

Am I short? Should I consider smaller PG only (impala, blesbok, warthogs, etc)?

FOC is 17 if that makes a difference (havent hit the magic 20 value.. but the arrows fly straight and consistent at the weight and FOC I currently have.. so I havent attempted to change anything)..

In-Depth Arrow Testing with The Ranch Fairy [PLUS: Kinetic Energy & Momentum Calculator!]

Use our Kinetic Energy (KE) and momentum calculator for your hunting arrows! PLUS, read why the Ranch Fairy says "heavy matters."

n1outdoors.com

 

[joker2400]

I used a similar setup back in 2018 and had excellent performance. I shot a wildebeest as well. My arrow buried itself in the far shoulder. All other animals had pass throughs.

I have never been a big fan of Montecs though.

My PG setup this year is my Bowtech Solution with Vector HMRs, ~650 TAW. I’m going to use a variety of broadheads, including the SS3, Megameat, Sevr, and the Vector VBS.

I am also taking a buffalo/giraffe arrow that is an FMJ DG which should weigh in around 1100 grains with my 250gn Iron Wills on them.

I look forward to reading your report

 

[C.W. Richter]

My son took his Hoyt 70ish lb to Namibia years back, and if i recall correctly his arrow weight was 760. I know the arrow was 600 because he was shooting 160 gr (modern day variant of the old Zwickey black diamond delta) broadheads. It did the job (a little too well in one instance, where the arrow flew straight through a warthog or oryx and just nicked another animal upon exit. I think the aforementioned setup just met the E requirements. I have a great video on ensuring your bow is set up correctly for Africa (you can overcompensate for a lighter arrow with a higher draw weight and vice-versa, to a degree) but I'll have to remember which one it is...? On the converse, he brought his bow (set up for whitetail at home; 65ish lbs, light arrow/broadheads) for PG in Namibia a few years prior and he put the bow AWAY after the inevitable occurred and carried his 375 thereon out. That minimum E requirement has its basis in fact.

 

[C.W. Richter]

The dark recesses say the bow energy test by PH was by Frikkie Du Toit for someone who was bowhunting lion in the Kalahari (i think it's the video with The Judge, Sgt. Ermey and a wealthy guy that apparently modeled himself after Gene Simmons. He had quite the mane after taking his 4th lion.)

 

[BSO Dave]

Reading older threads on AH however.. it looks like the recommended KE for medium PG is 70 KE (Im a good bit short.. and even if I crank my bow up to its max 70lb draw capability, the max KE value I get is 63.71..

Am I short? Should I consider smaller PG only (impala, blesbok, warthogs, etc)?

I would not get too hung up on the KE number if I were you.. KE is really an antiquated measurement for minimum archery requirements for most plainsgame.. Momentum is the most important criteria for good penetration.

At 65lbs of draw with a 600 grain arrow and the broadheads and shafts you are shooting should offer more than enough momentum to provide excellent penetration. Front of Center weight distribution is also a key factor in creating momentum.. Most arrow manufacturers recommend 10-15% FOC for hunting arrows. However, I have seen much better results coming from those arrow builds with 20% and above for hunting arrows.. If you have good arrow flight now, you probably don't need to change a thing.. However, you can experiment with an insert or outsert to easily increase your FOC.. I wouldn't hesitate to add another 25-50 grains which should only improve your arrow flight although you may have to adjust your sight pin to compensate for a mild drop in point of impact..

 

[Ryan]

65 pounds, 600 grains and 211 fps is not a speed demon, but it does sound like a late 80s early 90s rig. I used a PSE back in the late 90s with similar stats and it killed some decent stout hogs. And a lot of plains game went into the salt back in the 80s and 90s. Keep it efficient. While you are using a Montec, my preference would be a cut on contact head with four blades using smaller bleeder blades. Even Asby admitted they worked more efficiently than 3 bladed heads. Dirt Nap, Magnus, Iron Will, Kudu point, Zwickey, and on and on. Put them in the right spot and you'll have your kudu or gemsbok on the ground.

 

[mdwest]

Not quite 90’s….but yes… an old rig.. 2007 PSE Mach X…

I’m guessing i can get the bow up to 70lbs which will probably take it to somewhere in the 218 fps range with 600gr arrows and still shoot it accurately… but that’s maxing it out…. It’s got nothing left after that…

I’ve thought about bumping up the weight of the broad head… another 25gr would slow things down a bit more, but at the same time bump up the FOC and increase the momentum…

I might check out some quality 150gr broadheads and see how the sticks fly…

 

[Ryan]

Not quite 90’s….but yes… an old rig.. 2007 PSE Mach X…

I’m guessing i can get the bow up to 70lbs which will probably take it to somewhere in the 218 fps range with 600gr arrows and still shoot it accurately… but that’s maxing it out…. It’s got nothing left after that…

I’ve thought about bumping up the weight of the broad head… another 25gr would slow things down a bit more, but at the same time bump up the FOC and increase the momentum…

I might check out some quality 150gr broadheads and see how the sticks fly…

The rule of thumb for speed gain per pound is 2 fps/pound. So going up to 70 pounds of draw I bet you'll get at least 220 fps with the same arrow. Right there you've gained 5 foot pounds of KE and puts it right where my 2005 CP Oneida Eagle was on my first hunt in Namibia in 2011. Yours has an advantage with 65 grains more weight for a bit more monentum. Mine was at 67 lbs and I used 525 grain arrows at 235 fps with 125 grain Slick Trick Magnums. On my blue wildebeest in 2011 it got through a rib on one side and broke a rib and stopped on the hide on the other. So, from my experience you have the necessary penetration potential. After that it's all about shot placement. I helped clean it to see what damage was done. I hit a couple big blood vessels above the heart and deflated both lungs with that four blade head. You couldn't ask for much better.

 

[rookhawk]

I am probably WAY over thinking this... but based on my last experience bow hunting PG with a bow (under penetration on a wildebeest that resulted in a LONG track.. several miles over a 24 hour period of time).. I am wanting to make sure I get things absolutely right this time around (Im taking a bow back to SA in July with the intent of hunting a few species of PG)..

Im shooting an older PSE Mach X bow.. arrows are CE Piledrivers with G5 Montec broadheads.. total arrow weight is 602 gr..

Im currently shooting at 65lbs.. speed is reliably chrono'd at 211 fps (not a super fast bow)..

Using the linked KE and Momentum calculator below.. im getting a KE value of 59.45 and a Momentum value of .564

My gut tells me this should be more than enough to effectively and humanely hunt up to medium sized PG to include the "tough" ones like wildebeest, zebra, etc..

Reading older threads on AH however.. it looks like the recommended KE for medium PG is 70 KE (Im a good bit short.. and even if I crank my bow up to its max 70lb draw capability, the max KE value I get is 63.71..

Am I short? Should I consider smaller PG only (impala, blesbok, warthogs, etc)?

FOC is 17 if that makes a difference (havent hit the magic 20 value.. but the arrows fly straight and consistent at the weight and FOC I currently have.. so I havent attempted to change anything)..

In-Depth Arrow Testing with The Ranch Fairy [PLUS: Kinetic Energy & Momentum Calculator!]

Use our Kinetic Energy (KE) and momentum calculator for your hunting arrows! PLUS, read why the Ranch Fairy says "heavy matters."

n1outdoors.com

I like everything about your build except the G5 Montecs. Go with a single bevel, chisel tipped broadhead. Your KE worries go away because you've cut your drag and resistance in several ways:

1.) It has only two cutting edges (one per blade) whereas your Montec has 4 blades which means 8 cutting surfaces to provide resistance?

2.) As you know since you're quoting Ranch Fairy, a bent tip is what reduces penetration. The demonstrably strongest and least likely to curl broadhead is a two blade tanto-tipped broadhead.

3.) You're also worried about pass through and as you know, 4 blades stop when they hit things, and you're worried about KE for pass-through. A single bevel chisel tip is going to spin (drill and skate) on bone until it finds a place to slip through the ribs.


Iron Will single bevels, no bleeder. Recommend the 150gr so you have more weight up front rather than in the insert. If you want to go heavier, you can always make your arrows 650gr as well, then you've passed the bone breaking threshold.

 

[Ryan]

I like everything about your build except the G5 Montecs. Go with a single bevel, chisel tipped broadhead. Your KE worries go away because you've cut your drag and resistance in several ways:

1.) It has only two cutting edges (one per blade) whereas your Montec has 4 blades which means 8 cutting surfaces to provide resistance?

2.) As you know since you're quoting Ranch Fairy, a bent tip is what reduces penetration. The demonstrably strongest and least likely to curl broadhead is a two blade tanto-tipped broadhead.

3.) You're also worried about pass through and as you know, 4 blades stop when they hit things, and you're worried about KE for pass-through. A single bevel chisel tip is going to spin (drill and skate) on bone until it finds a place to slip through the ribs.


Iron Will single bevels, no bleeder. Recommend the 150gr so you have more weight up front rather than in the insert. If you want to go heavier, you can always make your arrows 650gr as well, then you've passed the bone breaking threshold.

The Montec is a 3 blade. Asby even mentions 4 has less drag then three. And Ranch Fairy had a video about him using a 3-bladed head as I recall. So I suppose we could all go round and round about this. Suffice it to say a cut on contact will help him under these ccircumstances.

 

[mdwest]

As an update... Ive been playing around with the bow a bit for the last few days.. poundage is up to 70 which has taken the speed to a consistent 219.. Ive been surprised in that POI for arrows at 20 yards has only changed a very small amount (Im about 1" higher now at the increased speed).. groups have actually tightened up a little bit as well (Im not sure if thats the bow.. or just me getting more practice in.. Im shooting about 50 arrows a day right now)...

602gr arrows at 219 fps gets me 64.05 KE and .585 Momentum..

Ive got some 150gr field points being delivered today as well as a 3 pack of 150 gr 2 blade stingers.. Im curious to see how they fly and what I think about them.. Im guessing I'll lose about 10 fps when I add 25gr to the total arrow weight.. assuming that is correct, there will actually negative impact to the KE and Momentum values (60.75 and .581 respectively).. but the impact to momentum seems pretty immaterial.. and the additional 25gr up front will improve FOC a bit (should take me to right at 18).. so Im guessing in terms of penetration there will be no real difference and the increased FOC should make the arrow fly a little more true, fly a little quieter, etc..

I did notice with the increase in speed.. even though we're only talking an additional 8 fps the arrows are a little louder, making a bit more of a hiss as they travel to the target.. the bow doesnt seem to be picking up any additional noise though

 

[firehuntfish]

Ive got some 150gr field points being delivered today as well as a 3 pack of 150 gr 2 blade stingers.. Im curious to see how they fly and what I think about them.. Im guessing I'll lose about 10 fps when I add 25gr to the total arrow weight.. assuming that is correct, there will actually negative impact to the KE and Momentum values (60.75 and .581 respectively).. but the impact to momentum seems pretty immaterial..

Hi Mr. West,

Increasing your total arrow weight should increase your momentum. Yes, it's true that you will lose some arrow speed by increasing total arrow weight, but it's a fair price to pay for the benefits of more momentum and increased penetration capabilities.

Regardless, rest assured that the current bow & arrow set up you have right now will work very well on most any plainsgame animal. If you were shooting a lower poundage bow (less than 60lbs.) and a shorter draw length, I would be much more concerned with optimizing the total arrow weight, the FOC, and tweaking every drop of terminal performance from your set-up as possible. But, with you shooting 65-70lbs and a 600 grain arrow that is in good tune, you really don't need to get too caught up in the numbers. You are already generating enough energy and momentum to achieve your performance needs. Bowhunters can sometimes drive themselves crazy with the numbers when there is really no need to do so.. Good luck!

 

[mdwest]

I cant seem to stop going down the proverbial rabbit hole... (the marginal performance of my bow/arrow combo on a wildebeest in 2017 is whats keeping me up at night..)..

I THINK I have finally built an arrow I am happy with for the upcoming hunt..

636 grain
20.18 FOC
300 spine
flies straight/true at 218 FPS. Consistent 2" groups at 20 yards, 3" groups at 30 yards, etc.. no fishtailing or corkscrewing at all, paper tuned/tested as close to perfect as can be achieved, etc..etc..

With my 69.25 lb draw (measured last night) the above gives me 67.05 KE and .615 Momentum.

I went with Victory VForce Gamer shafts, 150gr inserts, 150gr broadheads (Magnus Stinger 2 blade).

Assuming I do my part and put the stick where it belongs, I cant imagine any small to medium sized PG that my rig wont effectively kill.

Now I just have to get out and let 20-30 arrows fly 4 or 5 times a week for the next 8 weeks while I wait to travel...

The next blue wildebeest I stick should go down a whole lot easier than the last one..

 

[joker2400]

I cant seem to stop going down the proverbial rabbit hole... (the marginal performance of my bow/arrow combo on a wildebeest in 2017 is whats keeping me up at night..)..

I THINK I have finally built an arrow I am happy with for the upcoming hunt..

636 grain
20.18 FOC
300 spine
flies straight/true at 218 FPS. Consistent 2" groups at 20 yards, 3" groups at 30 yards, etc.. no fishtailing or corkscrewing at all, paper tuned/tested as close to perfect as can be achieved, etc..etc..

With my 69.25 lb draw (measured last night) the above gives me 67.05 KE and .615 Momentum.

I went with Victory VForce Gamer shafts, 150gr inserts, 150gr broadheads (Magnus Stinger 2 blade).

Assuming I do my part and put the stick where it belongs, I cant imagine any small to medium sized PG that my rig wont effectively kill.

Now I just have to get out and let 20-30 arrows fly 4 or 5 times a week for the next 8 weeks while I wait to travel...

The next blue wildebeest I stick should go down a whole lot easier than the last one..

That setup is adequate for eland and smaller

 

[rookhawk]

That setup is adequate. The broadheads are as good as you can buy at an archery shop, but literally the lowest quality two blade.

Better steel, single bevel, tanto tip, you’d need Iron Will single bevels. Those will break bone by design and were the best tested broadhead on Lusk outdoors reviews.

 

[mdwest]

Better steel, single bevel, tanto tip, you’d need Iron Will single bevels. Those will break bone by design and were the best tested broadhead on Lusk outdoors reviews.

I went back and forth with whether or not to invest in higher end, single bevel broadheads like Iron Will or Grizzly Stik, etc... And ultimately decided on the Stingers based on a couple of factors..

In total contradiction to my position on rifle ammo (where I routinely argue that ammo is the cheapest investment in the hunt.. so buy the best available for your intended purpose).. I did let price play into the equation here.. I purchased a dozen broadheads (4x packs of 3x Stingers = $128 vs 4x packs of Iron Will / Grizzly, etc = +/- $450).. I wanted enough broadheads that I could shoot the hell out of about a half dozen out of them between now and the hunt and make sure that the bow was tuned and accurate to the broadhead... knowing I'd dull and/or ruin many of those with hundreds of shots into rubber to the point where they wouldnt be practical for hunting.. and still have enough left over to take on the trip that would be perfectly fresh/new and ready to hunt... and since these arrows will only be used for South Africa, while I wanted something good, reliable, straight shooting, etc.. I also didnt want to invest a fortune into shafts, broadheads, etc on something that will get trained with extensively for 2 months.. then hunted with for 1 week.. and then likely not used again for several years... (Scot-Irish cheap part of my personality prevailed)..

I also wanted something that would be very easy to sharpen and maintain in the field.. This is going to sound ridiculous from a guy that is a hobbyist knife maker and spends several hours a month in his shop sharpening stuff made from steel.. but, Im not worth a crap at putting or maintaining an edge on a single bevel, regardless of the tool I am using... I can however take a reasonably sharp double bevel edge and get it to scalpel sharpness in a matter of just a couple of minutes.. With the little lansky broadhead sharpener, keeping a double bevel edge in hunting shape is pretty easy to do..

So I looked at probably a dozen different common Archery Shop quality broadhead options that fit the above.. read a ton of online reviews, etc.. and ultimately settled on the Stingers (most commonly had the highest reviews for penetration, consistent flight with field points, ease of maintenance, coming sharp out of the packaging, etc).. I initially just bought a 3 pack to give them a try.. shot them several times to see how they flew in comparison with the field points, how they chrono'd, how well they penetrated the targets, etc.. etc.. they seem to be doing exceptionally well... so I ordered 3 more packs (12 total)..

I fully concede that something like the Iron Will is better.. Im just banking on the Stingers being better than "good enough".. and that between them, the total arrow weight, FOC, momentum, KE, etc. being generated, that its a solid combination for what I most expect to shoot (theres nothing in particular on the menu.. but Im thinking most likely targets will end up being impala, warthog, blue wildebeest, zebra, kudu... and maybe a guinea fowl if they keep coming into the blind area and stirring up shit like they did the last time I bow hunted in South Africa )...

 

[rookhawk]

I went back and forth with whether or not to invest in higher end, single bevel broadheads like Iron Will or Grizzly Stik, etc... And ultimately decided on the Stingers based on a couple of factors..

In total contradiction to my position on rifle ammo (where I routinely argue that ammo is the cheapest investment in the hunt.. so buy the best available for your intended purpose).. I did let price play into the equation here.. I purchased a dozen broadheads (4x packs of 3x Stingers = $128 vs 4x packs of Iron Will / Grizzly, etc = +/- $450).. I wanted enough broadheads that I could shoot the hell out of about a half dozen out of them between now and the hunt and make sure that the bow was tuned and accurate to the broadhead... knowing I'd dull and/or ruin many of those with hundreds of shots into rubber to the point where they wouldnt be practical for hunting.. and still have enough left over to take on the trip that would be perfectly fresh/new and ready to hunt... and since these arrows will only be used for South Africa, while I wanted something good, reliable, straight shooting, etc.. I also didnt want to invest a fortune into shafts, broadheads, etc on something that will get trained with extensively for 2 months.. then hunted with for 1 week.. and then likely not used again for several years... (Scot-Irish cheap part of my personality prevailed)..

I also wanted something that would be very easy to sharpen and maintain in the field.. This is going to sound ridiculous from a guy that is a hobbyist knife maker and spends several hours a month in his shop sharpening stuff made from steel.. but, Im not worth a crap at putting or maintaining an edge on a single bevel, regardless of the tool I am using... I can however take a reasonably sharp double bevel edge and get it to scalpel sharpness in a matter of just a couple of minutes.. With the little lansky broadhead sharpener, keeping a double bevel edge in hunting shape is pretty easy to do..

So I looked at probably a dozen different common Archery Shop quality broadhead options that fit the above.. read a ton of online reviews, etc.. and ultimately settled on the Stingers (most commonly had the highest reviews for penetration, consistent flight with field points, ease of maintenance, coming sharp out of the packaging, etc).. I initially just bought a 3 pack to give them a try.. shot them several times to see how they flew in comparison with the field points, how they chrono'd, how well they penetrated the targets, etc.. etc.. they seem to be doing exceptionally well... so I ordered 3 more packs (12 total)..

I fully concede that something like the Iron Will is better.. Im just banking on the Stingers being better than "good enough".. and that between them, the total arrow weight, FOC, momentum, KE, etc. being generated, that its a solid combination for what I most expect to shoot (theres nothing in particular on the menu.. but Im thinking most likely targets will end up being impala, warthog, blue wildebeest, zebra, kudu... and maybe a guinea fowl if they keep coming into the blind area and stirring up shit like they did the last time I bow hunted in South Africa )...

@mdwest I understand what you are saying, I would leave you with a couple of counterpoints:

1.) Stingers are good, they just aren't as good as anything else we rattled off. What does that mean? They curl. curling loses penetration. My kids have killed plenty with them and certainly they are a wonderful, frugal white tail setup. (or elk) They fly great too.

2.) Single bevel broadheads are far easier to sharpen. You use a strop bat and strop compound. All you do is follow the angle of the bevel. Using a Lansky is stone-work. Where you are finishing your sharpness is where we start with ours. We take the broadheads out of the package and we strop them until super, super sharp. Far sharper than out of the box. They all dull just sititng in the quiver, so we strop them again every starting season.

3.) Yes, if you're shooting Magnus at a bag for tuning or practice, they will dull. Same with iron wills. The difference is that I can get a single bevel back to a razor for reuse, whereas a stinger shot into an animal is relegated to a target point thereafter.

Not ripping on your setup, I give it an A-. I think its the one part of your build you scrimped. You won't notice in the USA on deer, but you might on bigger stuff. The ferrules bend as well on the Magnus, its all we can expect for $40 for a pack of three.

 

[fourfive8]

The problem is the use of the wrong principle of physics for the assessment of effectiveness. A relatively low velocity, sharp pointed projectile like an arrow imparts near zero meaningful KE upon the media it impacts and penetrates. An arrow kills by cutting thus the physics of penetration and the broadhead's cutting ability both become paramount for effectiveness. Momentum is the key concept for assessing the penetration potential of an arrow and the correct index to be used for comparing effectiveness, on paper, among several options of equipment.

KE = 1/2 MVV
Momentum = MV

 

[Ryan]

I agree with you on sharpening, personally I can make a double bevel scalpel sharp far easier. But after the Stingers and their aluminum ferrule failed me about 20 years ago on a feral goat in Texas I went for steel ferrule broadheads and have never regretted it. Magnus Stingers actually made me go to Slick Tricks back then, and still using them. For a cut on contact I wish the Kudu point was easier to sharpen, I'd be using them more. But I couldn't get the whole edge consistently sharp. They do have a Lansky adapter now, so perhaps.

 

[Ryan]

If you haven't checked them out yet look up Vantage Point Archery broadheads. Here's their 150 grain 2 blade with double bevel edge. A bit more expensive at $67.50, but very strong and easy to sharpen on your Lansky. If I were to go with only two blade head for plains game that would be my choice.